S, is preferentially modified by human ART1 on R14 with an additional site at R24 (Paone et al. 2006; Paone et al. 2002; Stevens et al. 2009). Mouse P2X7 is modified by ART2.2 at R125 and at R133 (Adriouch et al. 2008) (Fig. 5). Of note, in both of these cases as well as in the case of the preferred site in HNP-1, the modified arginine is part of a di-arginine (RR) motif. In two of these sites (HN